An ESR and theoretical ab initio study of the structure and dynamics of the pyrrolidine radical cation and the neutral 1-pyrrolidinyl radical

Shiotani, Masaru; Sjoeqvist, L.; Lund, Anders; Lunell, Sten; Eriksson, Leif A.; Huang, Ming‐Bao

doi:10.1021/j100384a020

Cited by 33 publications

(13 citation statements)

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“…But with other types of radicals such as alkyl and alkoxy radicals and, to a lesser extend, alkylperoxy radicals, they react relatively rapidly under product formation (Eq. 22,23,25). This has been demonstrated in the pulse radiolysis of TEMPO solutions in organic solvents, under which conditions the mentioned radicals are generated.…”

Section: Mechanism Of Hals Stabilizer Actionmentioning

confidence: 89%

“…3) enabled the observation of the acceptor radicals A9 with optical spectroscopy 14) , whereas AH9 and AN9 have been detected by electron spin resonance spectroscopy 11,15) . Furthermore, amine radical cations have been detected in low temperature and matrix isolation experiments 14,[16][17][18][19][20][21][22] . Our own pulse radiolysis experiments on electron transfer from sterically hindered amines to solvent parent ions resulted in the case of secondary HALS in the optical detection of the corresponding amine radical cations 12,14) .…”

Section: Introductionmentioning

confidence: 99%

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Transformation of sterically hindered amines (HALS) to nitroxyl radicals: What are the actual stabilizers?

Brede¹,

Göttinger

1998

Angew. Makromol. Chem.

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Section: Mechanism Of Hals Stabilizer Actionmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Transformation of sterically hindered amines (HALS) to nitroxyl radicals: What are the actual stabilizers?

Brede¹,

Göttinger

1998

Angew. Makromol. Chem.

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“…Chemical Exchange The analysis of intramolecular motion of radicals in irradiated systems [125][126][127][128][129][130][131][132][133][134][135][136][137][138][139][140][141] has in general been made by comparison of experimental spectra recorded at different temperatures with simulations of spectra at different interchange rates between two or more geometric configurations. Procedures based on the Liouville formalism for the analysis of intramolecular motions in anisotropic systems have been developed [125][126][127][128][129][130][131].…”

Section: Motional Studies With Peroxy Spin Probesmentioning

confidence: 99%

“…This condition was found to approximately apply for the treatment of the dynamics in a number of irradiated frozen matrices. The temperature dependent spectra of cationic and neutral radicals [138][139][140][141] were for instance analyzed by the Heinzer method [142,143] for exchange-broadened isotropic EPR spectra. This method was also employed for the study of the intramolecular motion of radiation induced radicals trapped in zeolites [144][145][146].…”

Section: Motional Studies With Peroxy Spin Probesmentioning

confidence: 99%

Applications of EPR and ENDOR Spectrum Simulations in Radiation Research

Erickson

Lund

2014

Applications of EPR in Radiation Research

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Applications of EPR and ENDOR simulations of relevance in radiation research involving free radicals, radical pairs, triplet states and to less extent metal complexes are treated. Early fundamental work involving in situ radiolysis of liquids and stickplot analysis of spectra is reviewed, while single crystal analysis is only briefly discussed. The analysis of data obtained with continuous wave methods of species trapped in disordered solids, "powders" is emphasized. Simulations based on first and second order and exact theory are described and exemplified. Methods to obtain parameters for the dynamics of radicals in irradiated solids and for the simulation of spectra at microwave saturation are discussed. Procedures for the simulation of powder ENDOR spectra of radicals are described in detail, with special emphasis on the influence of nuclear quadrupole couplings due to nuclei with I ≥ 1. EPR and ENDOR simulation programs known to us are presented in an Appendix, including addresses for downloading when available.

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“…In some cases, as for the amine cation radicals reported here, measurements in the liquid state have not succeeded, while the badly resolved temperature-dependent spectra of triethylamine radical cation in CFC13 matrix only suggested a hindered rotation [1]. Furthermore, the intemal motion of molecular radicals, such as the cyclopentane, methylcyclohexane, 1,1-dimethylcyclohexane and pyrrolidinyl radical cations, and the neutral cyclopentyl and 1-pyrrolidinyl radicals have been successfully studied in halocarbon matrices [2][3][4][5][6][7][8][9][10] but no similar reports were found for the dynamics of smaller molecular radicals. It has therefore been difficult to obtain information of the electronic structure and the internal dynamics of these ions.…”

Section: Introductionmentioning

confidence: 99%

Structure and dynamics of radicals in zeolite matrices: ESR and theoretical studies

et al. 2003

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Amine radical cations of the type R3N "+ and [R3NCH2] "+, R = CH3, C2H5, C3H7, and nitric oxide, NO, have been used to probe the bonding to the surface and the dynamics of the radicals trapped in the confined space of cages or channels in the zeolite. Regular continuous-wave electron spin resonance (ESR) was employed to study the internal motion of the cation radicals formed by ~/-irradiation of amines and related ammonium ions, introduced during the synthesis of the zeolites A1-offretite, SAPO-37, SAPO-42 and AIPO4-5. The ESR spectra of [(CH3)3NCH2] " § radical cation in several studied systems changed reversibly with temperature, indicating dynamical effects. Free rotation about the >N-CH 2 bond of the [(CH3)3NCH2] "+ species was found to occur in the temperature range of 110 to 300 K, while the rotation about the >N-CH 3 bonds was hindered. The observations contima the theoretical prediction on the basis of density functional theory calculations, which indicate that the corresponding barriers ate of the order of 0.3 and 7 kJ/mol, respectively. The radical cations of the type R3N "+ with R = C:H 5, C3H 7 were found to undergo a different type of dynamics, involving a two-jump process of the methylene hydrogens next to the nitrogen. A cage or channel size effect on the stability and molecular dynamics was inferred in some cases. Pulsed ESR was employed to study the (NO)2 triplet-state dimers in Na-A type zeolite, with the purpose to resolve the interaction with surface groups, and to elucidate the role of the zeolite on stabilizing the triplet rather than the usual singlet state. Measurements performed at 5 K gave rise to Fourier transform spectra that were assigned to the dimer species interacting with one or more '3Na nuclei, with approximative parameters A(23Na) = (4.6, 4.6, 8.2) MHz and Q(Z3Na) = (-0.3, -0.3, 0.6) MHz for the hyperfine and nuclear quadrupote coupling tensors, respectively. The values are of similar magnitude as those determined for the NO---Na + complex. The stability of the triplet-state structure was attributed to an unusual geometric structure imposed by the zeolite matrix, with the N-O bonds along a line as in [O-N---Na+---N-O], which according to UHF ab initio calculations has a triplet ground state. 286W. Liu et al.

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An ESR and theoretical ab initio study of the structure and dynamics of the pyrrolidine radical cation and the neutral 1-pyrrolidinyl radical

Cited by 33 publications

References 0 publications

Transformation of sterically hindered amines (HALS) to nitroxyl radicals: What are the actual stabilizers?

Transformation of sterically hindered amines (HALS) to nitroxyl radicals: What are the actual stabilizers?

Applications of EPR and ENDOR Spectrum Simulations in Radiation Research

Structure and dynamics of radicals in zeolite matrices: ESR and theoretical studies

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